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United States Patent |
6,201,244
|
Ju
,   et al.
|
March 13, 2001
|
Bolometer including an absorber made of a material having a low
deposition-temperature and a low heat-conductivity
Abstract
A three-level infra-red bolometer includes an active matrix level, a
support level, a pair of posts and an absorption level. The active matrix
level includes a substrate having an integrated circuit, a pair of
connecting terminals and a protective layer covering the substrate. The
support level includes a pair of bridges, each of the bridges being
provided with a conduction line formed on top thereof, wherein one end of
the conduction line is electrically connected to the respective connecting
terminal. The absorption level includes a serpentine bolometer element
surrounded by an absorber made of silicon oxide (SiO.sub.2) or silicon
oxy-nitride (SiO.sub.x N.sub.y). Each of the posts includes an electrical
conduit surrounded by an insulating material and is placed between the
absorption level and the bridge, in such a way that the serpentine
bolometer element is electrically connected to the integrated circuit
through the electrical conduit, the conduction line and the connecting
terminal.
Inventors:
|
Ju; Sang-Baek (Seoul, KR);
Yong; Yoon-Joong (Seoul, KR)
|
Assignee:
|
Daewoo Electronics Co., Ltd. (Seoul, KR)
|
Appl. No.:
|
146256 |
Filed:
|
September 3, 1998 |
Current U.S. Class: |
250/338.1; 250/338.4; 338/18 |
Intern'l Class: |
H01L 031/09 |
Field of Search: |
250/338.1,332,338.4
338/15,18,17
|
References Cited
U.S. Patent Documents
5021663 | Jun., 1991 | Hornbeck | 250/349.
|
5286976 | Feb., 1994 | Cole | 250/349.
|
5397897 | Mar., 1995 | Komatsu et al. | 250/338.
|
5404125 | Apr., 1995 | Mori et al. | 338/18.
|
5572029 | Nov., 1996 | Walker et al.
| |
5629521 | May., 1997 | Lee et al. | 250/338.
|
5760398 | Jun., 1998 | Blackwell et al. | 250/332.
|
5789753 | Aug., 1998 | Gooch et al. | 250/349.
|
5811815 | Sep., 1998 | Marshall et al. | 250/370.
|
5939971 | Aug., 1999 | Yong | 338/15.
|
6028312 | Feb., 2000 | Wadsworth et al. | 250/351.
|
6034374 | Mar., 2000 | Kimura et al. | 250/370.
|
Foreign Patent Documents |
0534768 | Mar., 1993 | EP.
| |
Other References
International Search Report Apr. 9, 1999.
|
Primary Examiner: Hannaher; Constantine
Attorney, Agent or Firm: Pennie & Edmonds LLP
Claims
What is claimed is:
1. A three-level infra-red bolometer comprising:
an active matrix level including a substrate and at least a pair of
connecting terminals;
a support level provided with at least a pair of bridges, each of the
bridges including a conduction line, one end of the conduction line being
electrically connected to the respective connecting terminal;
an absorption level including an upper absorber, a lower absorber and a
bolometer element formed between the upper and the lower absorbers,
wherein the lower absorber including a first lower portion made of
SiO.sub.x N.sub.y and a second lower portion made of SiO.sub.2, and the
upper absorber including a first upper portion made of SiO.sub.2 and a
second upper portion made of SiO.sub.x N.sub.y ; and
at least a pair of posts, each of the posts being placed between the
absorption level and the support level and including an electrical conduit
surrounded by an insulating material, each end of the bolometer element of
the absorption level being electrically connected to the respective
connecting terminal through the respective electrical conduit and the
respective conduction line.
2. The bolometer of claim 1, wherein the bridges are made of SiO.sub.2 or
SiO.sub.x N.sub.y.
3. The bolometer of claim 1, wherein the absorption level further includes
an IR absorption coating.
4. The bolometer of claim 1, wherein the bolometer element is made of
titanium.
5. In a three-level infra-red bolometer, the improvement comprising:
an absorption level including an upper absorber part, a lower absorber part
and a bolometer element formed between the upper and the lower part,
wherein the lower part includes a first lower portion made of SiO.sub.x
N.sub.y and a second lower portion made of SiO.sub.2, and the upper part
includes a first upper portion made of SiO.sub.2 and a second lower
portion made of SiO.sub.x N.sub.y.
Description
FIELD OF THE INVENTION
The present invention relates to an infra-red bolometer; and, more
particularly, to a three-level infra-red bolometer including an absorber
made of a material having a low deposition-temperature and a low
heat-conductivity.
BACKGROUND OF THE INVENTION
Bolometers are energy detectors based upon a change in the resistance of
materials (called bolometer elements) that are exposed to a radiation
flux. The bolometer elements have been made from both metals and
semiconductors. In case of the metals, the resistance change is
essentially due to a variation in the carrier mobility, which typically
decreases with temperature. In contrast, greater sensitivity can be
obtained in high-resistivity semiconductor bolometer elements wherein the
free-carrier density is an exponential function of temperature; however,
thin film fabrication of semiconductor elements for the construction of
bolometers is a difficult task.
In FIGS. 1 and 2, there are shown a perspective view and a cross sectional
view illustrating a three-level bolometer 100, disclosed in U.S.
application Ser. No. 09/102,364 entitled "BOLOMETER HAVING AN INCREASED
FILL FACTOR". The bolometer 100 comprises an active matrix level 110, a
support level 120, at least a pair of posts 170 and an absorption level
130.
The active matrix level 110 has a substrate 112 including an integrated
circuit (not shown), a pair of connecting terminals 114 and a protective
layer 116. Each of the connecting terminals 114 made of a metal is located
on top of the substrate 112. The protective layer 116 made of, e.g.,
silicon nitride (SiN.sub.x), covers the substrate 112. The pair of
connecting terminals 114 are electrically connected to the integrated
circuit.
The support level 120 includes a pair of bridges 140 made of silicon
nitride (SiN.sub.x), each of the bridges 140 having a conduction line 165
formed on top thereof. Each of the bridges 140 is provided with an anchor
portion 142, a leg portion 144 and an elevated portion 146, the anchor
portion 142 including a via hole 152 through which one end of the
conduction line 165 is electrically connected to the connecting terminal
114, the leg portion 144 supporting the elevated portion 146.
The absorption level 130 is provided with a serpentine bolometer element
185 made of titanium (Ti), an absorber 195 made of silicon nitride
(SiN.sub.x) and an IR absorber coating 197 formed on top of the absorber
195. The absorber 195 is fabricated by depositing silicon nitride before
and after the formation of the serpentine bolometer element 185 to
surround the serpentine bolometer element 185.
Each of the posts 170 is placed between the absorption level 130 and the
support level 120. Each of the posts 170 includes an electrical conduit
172 made of a metal, e.g., titanium (Ti), and surrounded by an insulating
material 174 made of, e.g., silicon nitride (SiN.sub.x). Top end of the
electrical conduit 172 is electrically connected to one end of the
serpentine bolometer element 185 and bottom end of the electrical conduit
172 is electrically connected to the conduction line 165 on the bridge
140, in such a way that both ends of the serpentine bolometer element 185
in the absorption level 130 is electrically connected to the integrated
circuit of the active matrix level 110 through the electrical conduits
172, the conduction lines 165 and the connecting terminals 114. When
exposed to infra-red radiation, the resistivity of the serpentine
bolometer element 185 changes, causing a current and a voltage to vary,
accordingly. The varied current or voltage is amplified by the integrated
circuit, in such a way that the amplified current or voltage is read out
by a detective circuit (not shown).
There are certain deficiencies associated with the above described
three-level bolometer 100. When selecting the material for the absorber
195, it is important to consider the fabrication conditions, e.g.,
deposition-temperature, and the material characteristics, e.g.,
heat-conductivity. In the above described three-level bolometer 100, since
silicon nitride (SiN.sub.x) can be formed only at a relatively high
temperature, e.g., over 850.degree. C., titanium (Ti) constituting the
serpentine bolometer element 185 gets easily oxidized during the formation
of the absorber 195, which will, in turn, detrimentally affect the
temperature coefficient of resistance (TCR) thereof. Further, silicon
nitride (SiN.sub.x) has a relatively high heat-conductivity, reducing the
thermal isolation effect of the absorber 195 in the bolometer 100.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a
three-level infra-red bolometer including an absorber made of a material
that can be formed at a low temperature and has a low heat-conductivity.
In accordance with one aspect of the present invention, there is provided a
three-level infra-red bolometer, which comprises: an active matrix level
including a substrate and at least a pair of connecting terminals; a
support level provided with at least a pair of bridges, each of the
bridges including an conduction line, one end of the conduction line being
electrically connected to the respective connecting terminal; an
absorption level including a bolometer element formed between an upper
absorber and a lower absorber, the absorbers being made of silicon oxide
or silicon oxy-nitride; and at least a pair of posts, each of the posts
being placed between the absorption level and the support level and
including an electrical conduit surrounded by an insulating material, each
end of the bolometer element of the absorption level being electrically
connected to the respective connecting terminal through the respective
electrical conduit and the respective conduction line.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the present invention will
become apparent from the following description of the preferred
embodiments given in conjunction with the accompanying drawings, wherein:
FIG. 1 shows a perspective view setting forth an infra-red bolometer
previous disclosed;
FIG. 2 present a schematic cross sectional view depicting the infra-red
bolometer shown in FIG. 1;
FIG. 3 depicts a schematic cross sectional view setting forth a three-level
infra-red bolometer in accordance with the present invention; and
FIGS. 4A to 4B provide schematic cross sectional views depicting an
absorption level in accordance with two preferred embodiments of present
invention, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There are provided in FIGS. 3 and 4A to 4B a schematic cross sectional view
setting forth a three-level infra-red bolometer 200 and schematic cross
sectional views of an absorption level therein in accordance with two
embodiments of the present invention, respectively. It should be noted
that like parts appearing in FIGS. 3 and 4A to 4B are represented by like
reference numerals.
The inventive bolometer 200 shown in FIG. 3 comprises an active matrix
level 210, a support level 220, at least a pair of posts 270 and an
absorption level 230.
The active matrix level 210 has a substrate 212 including an integrated
circuit (not shown), a pair of connecting terminals 214 and a protective
layer 216. Each of the connecting terminals 214 made of a metal is located
on top of the substrate 212. The pair of connecting terminals 214 are
electrically connected to the integrated circuit. The protective layer 216
made of, e.g., silicon nitride (SiN.sub.x) covers the substrate 212.
The support level 220 includes a pair of bridges 240 made of an insulating
material, e.g., silicon oxide (SiO.sub.2) or silicon oxy-nitride
(SiO.sub.x N.sub.y), each of the bridges 240 having a conduction line 265
formed on top thereof. Each of the bridges 240 is provided with an anchor
portion 242, a leg portion 244 and an elevated portion 246, the anchor
portion 242 including a via hole 252 through which one end of the
conduction line 265 is electrically connected to the connecting terminal
214, the leg portion 244 supporting the elevated portion 246.
The absorption level 230 is provided with an absorber 295 made of an
insulating material, a serpentine bolometer element 285 made of a metal,
e.g., titanium (Ti), and an IR absorber coating 297 positioned on top of
the absorber 295.
The table below provides the deposition-temperature and heat-conductivity
for the materials that can be used as the material for the absorber 295.
deposition- heat-conductivity
material temperature(.degree. C.) (W/m .multidot. .degree. C.)
SiN.sub.x 850 19
SiO.sub.2 200 1.3-1.8
SiO.sub.x N.sub.y 300 10.1-10.4
As shown in the above table, silicon oxide (SiO.sub.2) and silicon
oxy-nitride (SiO.sub.x N.sub.y), respectively, has a lower
heat-conductivity and a deposition-temperature than those for silicon
nitride (SiN.sub.x).
In the first embodiment of present invention, the absorber 295 includes a
lower part 310 and an upper part 320 which are made of an insulating
material, e.g., silicon oxide (SiO.sub.2) or silicon oxy-nitride
(SiO.sub.x N.sub.y), as shown in FIG. 4A.
As shown in FIG. 4B, a second embodiment is similar to the first
embodiment, except that an upper and a lower parts 310, 320 consist of two
layers. The lower part 310 includes a first lower portion 312 made of
silicon oxy-nitride (SiO.sub.x N.sub.y) and a second lower portion 314
made of silicon oxide (SiO.sub.2). The upper part 320 includes a first
upper portion 322 made of silicon oxide (SiO.sub.2) and a second upper
portion 324 made of silicon oxy-nitride (SiO.sub.x N.sub.y).
Each of the posts 270 is placed between the absorption level 230 and the
support level 220. Each of the post 270 includes an electrical conduit 272
made of a metal, e.g., titanium (Ti) and surrounded by an insulating
material 274 made of, e.g., silicon nitride (SiN.sub.x). Top end of the
electrical conduit 272 is electrically connected to one end of the
serpentine bolometer element 285 and bottom end of the electrical conduit
272 is electrically connected to the conduction line 265 on the bridge
240, in such a way that both ends of the serpentine bolometer element 285
in the absorption level 230 is electrically connected to the integrated
circuit of the active matrix level 210 through the electrical conduits
272, the conduction lines 265 and the connecting terminals 214. When the
infra-red energy is absorbed, the resistivity of the serpentine bolometer
element 285 is increased, in such a way that the increased resistivity is
read out by a detective circuit (not shown).
In the three-level infra-red bolometer 200 of the present invention, the
absorber 295 is made of a material having a relatively low heat
conductivity and low deposition temperature, e.g., siliconoxide
(SiO.sub.2) or silicon oxy-nitride (SiO.sub.x N.sub.y). The low deposition
temperature will prevent the bolometer element from getting oxidized
during the formation thereof and the low conductivity will increase the
thermal isolation effect of the absorber 295, which will, in turn,
facilitate in ensuring an optimum performance of the bolometer 200, e.g.,
a responsivity, a detectivity and a noise equilibrium temperature
difference (NETD).
While the present invention has been described with respect to certain
preferred embodiments only, other modifications and variations may be made
without departing from the scope of the present invention as set forth in
the following claims.
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